This invention relates to a composition and method of treating solder plated printed circuits and other metal surfaces to remove oxidation and foreign contaminants. The invention further includes the deposition of a non-oxidizable film on the cleaned surface.
The removal of solder, oxides and other contaminants from a plated surface is known. The cleaning agent usually comprises a strong mineral acid. These acids may include hydrochloric, sulfuric and fluoboric acid. In addition phosphoric acid may be used mixed with a carbohydrate.
Referring to the prior art, Beach U.S. Pat. No. 3,450,577 relates to a cleaner-coater composition for treating metal surfaces which contains an alkali metal phosphate and sugar. The sugar disclosed may be disaccharide such as sucrose, maltose and others.
Cook et al U.S. Pat. No. 3,296,149 discloses a corrosion inhibiting composition comprising a mixture of molasses, potassium iodide and a metal salt of a fatty acid. Phosphoric acid may be included in the composition.
The Fisher U.S. Pat. No. 3,249,547 also discloses a corrosion inhibiting orthophosphoric acid composition containing molasses. Still another patent containing orthophosphoric acid and molasses is U.S. Pat. No. 1,935,911 -- Neilson.
The use of phosphoric acid having a high P.sub.2 O.sub.5 content is known in electroless plating compositions as shown by Applicant's U.S. Pat. No. 3,689,292. The patent is directed to the provision of a lustrous adherent tin plate on a base metal.
In his patent invention the Applicant adds additional succinic or other dibasic acid to his cleaning composition. The original super phosphoric acid may contain about 0.2 grams of succinic acid. The additional dibasic acid adds longer life to the bath and results in a better cleaning action due to the tie up of undesirable ions such as copper.